Over the past several years, the need for limiting stack gas emissions at industrial facilities which process hazardous waste has become a topic of increasing importance. Government regulations are now pending for boilers and industrial furnaces burning hazardous waste as fuels or for recycling and methodology for continuous emissions monitoring systems (CENS) is currently being evaluated.
Among the compounds for which emissions limits will be set are HCl, SO.sub.2 and nitrogen oxides, NO.sub.x. At the present time, only a limited number of CEMS for HCl are installed in industrial environments and, as noted by Buonicore in "Experience with Air Pollution Control Equipment and Continuous Monitoring Instrumentation on Hazardous Waste Incinerators," Journal of Hazardous Materials, 1989, Vol. 22, pp. 233-242, the reliability of these systems has yet to be proven.
In December of 1989, the USEPA requested comments on "whether continuous emissions monitoring for HCl would be a feasible, practical requirement in lieu of waste analysis for chlorine to limit HCl emissions." The ASME Research Committee on Industrial and Municipal Wastes responded that only one of five monitoring devices found by the EPA to be "acceptable" was actually reliable in plant operations. The Committee noted that service and support on the device, which is based on infrared technology and produced in West Germany, has been inadequate to date. The Committee therefore concluded that continuous monitoring for HCl may be appropriate at large facilities but is inappropriate at smaller facilities.
A number of parameters in stack gas emissions can be used to evaluate the totality of the combustion process and the adequacy of the emission control system. For example the amounts of O.sub.2 CO.sub.2, SO.sub.2 and nitrogen oxides, NO.sub.x, present can indicate if the thermal degradation process is complete. See Oppelt "Incineration of Hazardous Waste, A Critical Review," Journal of Air Pollution Control and Waste Management, 1987, Vol. 37, No. 5, pp. 558-586, and C. Lee et al., "An Overview of Hazardous/Toxic Waste Incineration," Journal of Air Pollution Control and Waste Management, 1986, Vol. 36, No. 5, pp. 922-931, for reviews of the usefulness of these gases as indicators and the CEMS technology currently available for their measurement.
Products of incomplete combustion (PICs) are also components in stack gas for which public concern is high due to their potential toxicity. As noted by K. Lee in "Research Areas for Improved Incineration System Performance," Journal of Air Pollution Control and Waste Management, 1989, Vol. 38, No. 12, pp. 1542-1550, their formation and emissions of PICS are not well understood. Continuous monitors are not yet commercially available although Overton, "Development of Real-Time Stack-gas Analysis Methods," Journal of Hazardous Materials, 1989, Vol. 22, pp. 187-194, recently reported on a microbore gas chromatographic method which appears promising.
Continuous data for SO.sub.2 and HCl emissions can help insure that these gases are adequately neutralized by the scrubbing system. As noted by Podlenski in "Feasibility Study for Adapting Present Combustion Source Continuous Monitoring Systems to Hazardous Waste Incinerators," EPA Report No. 600/8-84-011a, 1984, such data can provide information that can be used as a guide for design and operation purposes. At the present time, however, the EPA accepted technology for HCl monitoring is a manual sampling method with subsequent laboratory analysis by either titration or ion chromatography.
In order to improve performance at industrial facilities processing hazardous waste and to monitor stack gas emissions for the purpose of risk assessment, there has been a longstanding need for a CEMS which efficiently monitors exhaust gases, especially HCl.
A CEMS consists of two major subsystems, an analytical subsystem and a sample extraction subsystem, each of which must be considered in the development of a complete system for continuous stack gas measurement. A variety of analytical technologies including gas chromatography, fourier transform infrared spectroscopy, photoacoustic spectroscopy, ion mobility spectrometry and mass spectrometry were evaluated and a commercially available mass spectrometer was chosen as the analytical subsystem. The advantages and disadvantages of the technologies mentioned above for this intended purpose has been discussed by Harlow et al., "Design of a Continuous Emissions Monitoring System at a Manufacturing Facility Recycling Hazardous Waste," Proceedings, Hazardous Materials Control Research Institute, Great Lakes 90, Cleveland, Oh., pp. 285-289, 1990.
As noted previously, use of CEMS to monitor compounds such as O.sub.2 and nitrogen oxides, NO.sub.x is known. These compounds can be delivered to an analytical instrument while allowing the stack gas to cool since they are gases at routine ambient temperatures. In addition, none of these substances are very reactive, making sample extraction systems for these compounds relatively straight forward. There is no need for a heated system and most particulate material is removed with the water. However, conventional CEMS sample extraction is unsatisfactory for compounds such as HCl.